Presented for hypothetical discussion only, without further comment:
"Many philosophers and scientists have either argued or assumed that consciousness is inherently private, and hence that one's own experience is unknowable to others. While language may allow humans to cross this supposed gap by communicating their experience to others, this is allegedly not possible for other animals."
-- From "Animal Consciousness" at section 1, First published Sat Dec 23, 1995; substantive revision Fri Apr 11, 2014, available on-line at Stanford Encyclopedia of Philosophy,
http://plato.stanford.edu/entries/consciousness-animal/